Through the eye of a needle, a world writ small. In this award-winning image, wildlife photographer Peter Parks depicts a single drop of seawater collected at the Great Barrier Reef in Australia and magnified 20 times to reveal its living contents.

WATER, WATER EVERYWHERE

The world's oceans cover 71 percent of the Earth's surface and contain 97 percent of its water. That equates to 361.2 quintillion gallons of ocean water, or roughly 22,200,000,000,000,000,000,000,000 drops of seawater.

IT'S ELEMENTAL

Oxygen and hydrogen are the most common elements in seawater. But most of the 118 known elements can be found in the world's oceans, from aluminum to zirconium.

SALINE SOLUTION

Typical salinity for seawater is 3.5 percent, with a normal pH of 8. However, both can vary by location. The saltier the seawater, the higher its density. The colder the seawater, the higher its density. The Pacific Ocean tends to be less dense than the Atlantic.

DEEPER FREEZE

SALT ADDED

Sea salt is more than just chloride and sodium. It also contains ions of sulfate, magnesium, calcium, potassium, bicarbonate, bromide, borate, strontium and fluoride.

LIQUID GOLD

Much is made about how much gold exists in the oceans: By some estimates, 25 billion ounces, which would be eight times more than all of the gold unearthed by humans in recorded history.

The trick is extracting it. Gold is widely dispersed throughout the oceans, with a dilute concentration of just 5 to 50 parts per trillion. That's comparable to a protozoan-sized speck in a quart of water.

By one reckoning, you would need to filter 100 million tons of seawater to produce a single gram of gold.

THIN-SKINNED

The “air-sea interface” lies where the Earth's atmosphere rests upon its oceans. It is arguably the most physically and chemically active environment on the planet.

Here, a filmy layer no thicker than a millimeter churns with proteins, amino acids, sugars, fatty acids, minerals, metals, man-made compounds and life. At the interface, the atmosphere and oceans ceaselessly swap gases, liquids and solids.

For example, oxygen and carbon dioxide are constantly dissolving into the water. In fact, the ocean stores 93 percent of the Earth's CO2, 50 times more than exists in the atmosphere. Rising levels of atmospheric carbon dioxide mean more CO2 in seawater and increased ocean acidity, which eats away at the calcium carbonate skeletons of corals and some plankton.

Simultaneously, ocean evaporation provides 86 percent of the atmosphere's moisture. And hundreds of thousands of tons of sea salt and microorganisms are hurled aloft annually by crashing waves, spray and bursting bubbles. Some of this material forms the nuclei of water droplets and aids in cloud formation.

HEAT SINK

The surface zone of the ocean, which contains the warmest, least dense water and greatest abundance of life, extends 320 to 1,650 feet deep. Yet it represents just 2 percent of the oceans' volume. The upper few feet of the ocean contains as much heat as the entire atmosphere. Indeed, the world's oceans are a fantastic heat sink. If the sun turned off tomorrow, it would take approximately five years for the mean temperature of the ocean to fall 1 degree Celsius.

WANDERING WONDERS

Plankton (Greek for “wandering”) are creatures found throughout the world's oceans. They cannot swim. Most simply drift with currents, though some species can move up and down in the water column.

Phytoplankton are plants, the primary generators of oceanic photosynthesis and atmospheric oxygen, and the foundation of aquatic food webs. They provide meals for zooplankton, animals that range from protozoa and worms to jellies and fish larvae.

No one knows exactly how many plankton species exist. The total number is in the tens of thousands. Almost 6,800 species of zooplankton alone have been described.

LIFE-SIZED

Plankton are defined by size. The smallest are picoplankton, less than 2 microns in size, comparable to smoke particles. Picoplankton are viruses and bacteria.

The largest known plankton is the lion's mane jellyfish, whose bell can reach 8 feet in diameter, with tentacles exceeding 100 feet in length.

BIO-MASSED

Plankton make up a major portion of the Earth's total biomass. The smallest free-living cell known, a marine bacterium called SAR11, is so plentiful in the ocean that its combined weight exceeds that of all the fish in the sea.

As a group, copepods – tiny crustaceans, many planktonic – form the largest animal biomass. And the Antarctic krill, a shrimplike crustacean, represents the biggest biomass of a single species: an estimated 500 million tons, or 0.7 percent of the Earth's entire biomass.

MANY WORLDS

The “paradox of the plankton” is an old conundrum asking how so many diverse organisms can co-exist in a supposedly homogenous, resource-limited habitat. The phenomenon defies Gause's Law, a biological principle that says when two or more species compete for the same resource, one prevails and the other goes extinct.

In fact, scientists now know the upper layer of seawater, where most plankton reside, is not uniform, but parsed into countless changing micro-niches by variations in temperature, light, weather, predation, disease and more.